The invention relates to electronic reproduction technology, particularly to the production of corrected and retouched color separations by means of an electronic image processing system (retouch station).
In electronic reproduction, three primary color signals are acquired in a color scanner by means of image point-by-image point and line-by-line, opto-electronic scanning of an original color image. These primary color signals represent the color components red, green, and blue of the scanned image points. A color correction computer corrects the primary color signals and generates the color separation signals required for the production of the color separations therefrom. These color separation signals are a measure for the amounts of printing ink required in the later print. The color separation signals are digitized and stored in a storage medium image point-by-image point as digital color values.
In an image processing system, the stored digital color values of various individual originals can be united according to a layout plan into the dataset of an entire page and/or can be altered for the execution of a subsequent, partial retouch.
In order to record the color separations, the altered digital color values are read out from the storage medium, are converted back into analog color separation signals and are supplied to a recorder in which the rastered or unrastered color separations "magenta", "cyan", "yellow" and "black" are exposed for the production of the printing forms.
A method for partial, electronic retouch is already specified in U.S. Pat. No. 4,393,399, incorporated herein by reference, wherein the digital color values are altered image-point-wise, and partially in accordance with the desired retouch effects in the color image or in the color separation under visual control on a color monitor. The image point coordinates of the color values to be retouched and the desired degree of retouch are defined with the assistance of a marker means in the form of a coordinate pen of a coordinate identification means such that the retoucher guides the coordinate pen similar to a retouch brush over the image part to be retouched.
It can occur in reproduction that the original color image is already damaged in certain parts or that it is damaged during the reproduction process. The retoucher must then attempt to regenerate the damaged image parts of the color image by means of retouching. The success of such a retouch is very imperfect with conventional brush retouching and with the known electronic retouch method, particularly when the damaged image part exhibits a wealth of detail such as, for example, a herringbone pattern.